The present invention relates to electrodes whose main material is lanthanum and nickel alloys, which can be called nickel lanthanide, and to their use. It is known that nickel lanthanides whose composition is close to the formula La Ni.sub.5 fix hydrogen, forming hydrides which can then give up their hydrogen by a reversible reaction.
It has been proposed to use these nickel lanthanides in alkaline secondary cells of the nickel or silver-hydrogen type for example, in order to lower the hydrogen pressure during operation. It has been observed that electrodes which are cathodically polarized and hence charged, to several times their theoretical capacity (counting six or seven atoms of hydrogen for the formula La Ni.sub.5), yielded a capacity of about 92% of the theoretical capacity at 0.degree. C. and in concentrated electrolyte (12M potassium hydroxide); but it has been observed that this efficiency fell to 83% at ambient temperature and became only 50 to 60% in 5M potassium hydroxide.
Preferred embodiments of the present invention are intended to improve the capacity of such electrodes whatever the temperature and electrolyte concentration conditions.
The present invention provides an electrode whose main material is nickel lanthanide for use in an alkaline electrolyte, to which material a mercury compound is added.
Preferably, the compound is mercury oxide HgO and the weight of HgO added to the lanthanide is equal aproximately to 2% of the weight of the lanthanide.
The invention will be better understood by referring to the following detailed descriptive example of the electrode embodying the invention and its use.